Sludge treating apparatus

Abstract

A sludge treating apparatus comprises a centrifugal condensing machine for forcedly condensing a raw sludge produced by a waste water treating apparatus. The raw sludge condensed to approximately 94 to 90% in terms of the percentage of moisture content by means of the centrifugal condensing machine is introduced into an anaerobic digestion tank of a deep well type, where the raw sludge undergoes an anaerobic digestion, and a digested sludge obtained from the anaerobic digestion tank is then dewatered by means of a dewatering apparatus such as a belt press, whereupon the dewatered sludge is applied to a post-treatment apparatus. In execution of the anaerobic digestion process, the reactions corresponding to an acid fermentation stage and acid regression stage may be carried out in advance in separate tanks and the reaction corresponding to an alkaline fermentation stage may be mainly performed in an anaerobic digestion tank.

What is claimed is: 
     
       1. An apparatus for treating a sludge produced by waste water treatment, comprising: mechanical condensing means (17) for forcedly condensing a produced raw sludge, an anaerobic digestion tank (23) of a deep well type buried to extend under the ground in the depth direction, fluid conduit means operatively connecting said digestion tank to said condensing means for receiving and anaerobically digesting the raw sludge condensed by said mechanical condensing means, said anaerobic digestion tank comprising a downward flow chamber extending in the depth direction for flowing a sludge being treated downwardly therethrough, an upward flow chamber disposed in association with said downward flow chamber and also extending in the depth direction, fluid communication means between said upward flow chamber and said downward flow chamber for flowing a sludge being treated therethrough in the upward direction, circulating means operatively connected to said downward flow chamber and said upward flow chamber for forcedly circulating the sludge being treated between said downward flow chamber and said upward flow chamber and for expediting the reaction in said anaerobic digestion tank, and enclosure means for maintaining said digestion tank in an anaerobic condition, whereby conversion from fatty acid into methane gas and carbon dioxide takes place during the anaerobic digestion in said tank with simultaneous conversion from said carbon dioxide into methane gas as a result of the static pressure head afforded by the deep well location of said anaerobic digestion tank, said apparatus further comprising dewatering means operatively connected to said anaerobic digestion tank for receiving and dewatering the sludge digested by said anaerobic digestion tank, methane gas collecting means operatively connected to said anaerobic digestion tank for collecting methane gas produced in said anaerobic digestion tank, and post-treatment means operatively connected to said dewatering means for further treating the digested sludge after the sludge has been dewatered by said dewatering means, said post-treatment means comprising heat generating means, means operatively connected to said methane gas collecting means for supplying said methane gas collected by said methane gas collecting means to said post-treatment means as a source of energy for said heat generating means. 
     
     
       2. The sludge treating apparatus of claim 1, further comprises a separate tank interposed between and fluidly communicating with said mechanical condensing means and said anaerobic digestion tank for performing a reaction corresponding to an acid fermentation and an acid regression, and wherein said anaerobic digestion tank substantially performs an anaerobic digestion corresponding to an alkaline fermentation. 
     
     
       3. The sludge treating apparatus of claim 2, wherein said separate tank comprises closure means to form a further anaerobic tank. 
     
     
       4. The sludge treating apparatus of claim 1, wherein said anaerobic digestion tank of the deep well type is buried extending under the ground in the depth direction deeper than 10 m for providing a respective static pressure head in said anaerobic digestion tank. 
     
     
       5. The sludge treating apparatus of claim 4, wherein said anaerobic digestion tank is buried extending under the ground in the depth direction to a depth in the range of 10 m to 100 m. 
     
     
       6. The sludge treating apparatus of claim 1, further comprising: stirring means for stirring the sludge being treated in said anaerobic digestion tank for expediting the reaction in said anaerobic digestion tank. 
     
     
       7. The sludge treating apparatus of claim 6, wherein said stirring means comprises rotational stirring means for stirring the sludge being treated through rotation thereof. 
     
     
       8. The sludge treating apparatus of claim 6 or 7, wherein said stirring means comprises fixed stirring means fixedly provided at a portion of said upward flow chamber. 
     
     
       9. The sludge treating apparatus of claim 1, wherein said anaerobic digestion tank comprises a downward flow tube constituting said downward flow chamber, and an upward flow tube for forming said upward flow chamber together with said downward flow tube. 
     
     
       10. The sludge treating apparatus of claim 9, wherein said downward flow tube is disposed in said upward flow tube. 
     
     
       11. The sludge treating apparatus of claim 10, further comprising: heat insulating means provided outside said upward flow tube.